1. Field of the Invention
This invention relates to methane gas in coal mines, and more particularly to a method and apparatus for eliminating methane gas from boreholes.
2. Related Art
Methane emanates naturally from coal seams and the surrounding geological strata, and is a significant mine safety hazard. Various studies have been conducted to determine how to dispose of this methane gas and whether the methane can be advantageously utilized.
The methane present within the working areas of a coal mine is often removed through the drawing of fresh air into the work areas by large ventilation systems. These systems function to dilute and withdraw the methane gas. In some cases, ventilation alone proves ineffective in controlling methane concentrations in the deepest and most intricate mines such that other means of removing methane become necessary. One method for dealing with this problem is to drill xe2x80x9cdrainage holesxe2x80x9d into a coal seam prior to the actual mining operation. These drainage holes can yield significant quantities of relatively pure methane, sometimes up to 90 percent by volume while reducing the emission rate of methane in the ventilation air.
The concentration of methane in the air stream created by ventilation systems is oftentimes very dilute, and as a result conventional combustion systems are unable to take advantage of this abundant source of energy. Various other means of utilizing this large, but low concentration by volume of methane gas have been considered, but to date, none has been widely adopted. First, spark ignition engines are potentially able to convert the chemical energy in the methane/air mixture to useful energy, but this technology is not well suited for the task due to the inability of such engines to operate with mixtures below the lean limit thus necessitating large quantities of supplemental fuel. A second alternative is to use a gas turbine engine. However, these engines would also require a substantial quantity of supplemental fuel along with the energy required to compress the supplementary fuel to the operating combustion pressure. A final suggested design alternative is the use of regenerative thermal oxidizers; however, such systems have a relatively high pressure drop and generally operate on a reciprocal flow operation, which presents problems associated with the design of how to connect these units to the ventilation fan ducts.
Various attempts have been made in the coal mining industry to modify spark ignition engines to allow them to run on methane gas extracted from borehole air streams. However, these attempts have resulted in systems with engines that are unable to run when the air stream is less than about 65% to about 70% methane. Additionally, because the air stream generated from the boreholes often contains a significant amount of moisture, these systems are also often inoperable in cold weather conditions because the moisture in the air stream freezes. Therefore, a need exists to design a methane gas control system having an engine that continues to run when there is only a low quality methane source available. There is a further need for a system that is sufficiently rugged to function during inclimate weather, especially freezing conditions.
The present invention solves the problems encountered with previous methods of regulating methane gas by providing a methane gas control system with a methane-fueled engine that is capable of running when the air stream is as little as 30% methane. The invention further provides a methane gas control system that is operational in all weather conditions, including freezing weather.
One aspect of the invention is a methane gas control system for eliminating methane gas from a source, including a blower having an inlet for generating an air stream from the source and a discharge section for expelling the air stream from the blower, a fuel collector attached to the discharge section of the blower for collecting methane gas contained in the air stream, a heated dryer connected to the fuel collector for eliminating moisture from the methane gas, and an engine connected to the heated dryer that is at least partially fueled by the methane gas.
Another aspect of the invention is a method of removing methane from a source, including the steps of (a) generating and collecting an air stream containing methane gas from the source with a blower; (b) collecting the methane gas contained in the air stream in a fuel collector; (c) removing moisture from the methane gas with a heated dryer; and (d) transporting the methane gas from the heated dryer to an engine that is at least partially fueled by the methane gas.
Another aspect of the invention is a method of maintaining a desired air to fuel ratio in a spark ignition engine fueled at least partially by methane gas, including the steps of (a) regulating methane gas flow through a primary methane fuel line and into the engine with a methane control valve; and (b) regulating atmospheric air flow into the engine by closing a special choke mounted on the engine carburetor.
A feature of the invention is a heated dryer that removes moisture from methane gas contained in an air stream collected from a source.
Another feature of the invention is that the heated dryer remains at a steady temperature thereby preventing freezing of the methane gas.
Another feature of the invention is a methane control valve for regulating the amount of methane gas metered to the engine.
Another feature of the invention is a special choke for regulating the atmospheric air to the engine.
Another feature of the invention is an LP gas system that enables the methane gas control system to remain operational when methane gas is present in very low concentrations, or when the methane gas that is present is of very poor quality.
Another feature of the invention is the simultaneous regulation of atmospheric air and methane gas to the engine.
An advantage of the invention is that the heated dryer collects moisture from the air stream containing the methane gas and expels the collected moisture automatically.
Another advantage of the invention is that the engine is capable of running on at least about 300 BTU methane gas.
Another advantage of the invention is that the methane gas control system remains highly operational while requiring minimal maintenance.
Another advantage of the invention is the improved ability to regulate air to fuel ratio due to a methane control valve for regulating methane flow to the engine, a special choke for regulating the flow of atmospheric air to the engine, and a secondary methane fuel line that bypasses the special choke for adding a mixture of air and methane gas to air/fuel mixture.